Ostwald Ripening Disproportionation

This results from the finite solubility of the liquid phases. Liquids which are referred to as being immiscible often have mutual solubilities which are not negligible. In the case of emulsions, which are usually polydisperse, the smaller droplets will have a greater solubility compared to the larger droplets (due to curvature effects). With time, however, the smaller droplets will disappear and their molecules will diffuse to the bulk and become deposited on the larger droplets. With time, the droplet size distribution wiU shift to a larger value. 

This refers to the process of thinning and disruption of the liquid film between the droplets, with the result that two or more droplets fuse into a larger droplet. The limiting case for coalescence is the complete separation of the emulsion into two distinct liquid phases. The driving force for coalescence is the surface or film fluctuations this results in a close approach of the droplets whereby the van der Waals forces are strong and prevent their separation. 

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These are dispersions of liquid drops in an immiscible liquid medium. The most common systems are oil-in-water (O/W) and water-in-oil (W/O). It is also possible to disperse a polar liquid into an immiscible nonpolar liquid, and vice versa these are referred to as oil-in-oil (0/0) emulsions. In order to disperse a liquid into another immiscible liquid, a third component is needed that is referred to as the emulsifier. Emulsifiers are surface-active molecules (surfactants) that adsorb at the liquid/liquid interface, thus lowering the interfacial tension and hence the energy required for emulsification is reduced. The emulsifier plays several other roles (i) it prevents coalescence during emulsification (ii) it enhances the deformation and break-up of the drops into smaller units (iii) it prevents flocculation of the emulsion by providing a repulsive barrier that prevents close approach of the droplets to prevent van der Waals attraction (iv) it reduces or prevents Ostwald ripening (disproportionation) (v) it prevents coalescence of the drops and (vi) it prevents phase inversion. 

Another mechanism of foam instability is due to Ostwald ripening (disproportionation), the driving force for which process is the difference in Laplace pressure between the small and larger foam bubbles. The smaller bubbles have a higher... 

Surface Dilational Properties. The calculations just given suggest that all foam will rapidly disappear, but several foams can be fairly persistent, and some can hardly be destroyed. Stabilization to Ostwald ripening (or to disproportionation as foam researchers usually call it) is thus possible. 

Destabilization of gas bubbles may occur as a result of two different mechanisms. The first is disproportionation or Ostwald ripening. Pressure inside a small gas bubble is greater than that outside due to the effect... 

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